Melanin protects skin against ultraviolet radiation-induced damage, thus reducing risk of cutaneous cancers. Our primary objective is to elucidate the mechanisms that regulate melanin synthesis and characterize the pathogenesis of pigmentary disorders. We will focus on tyrosinase, the enzyme that catalyzes the first, rate-limiting step in melanin synthesis, namely conversion of L-tyrosine to dihydroxyphenylalanine. Tyrosinase is a determinant of skin pigmentation and risk of cutaneous cancers. Tyrosinase has also been implicated in genetic disorders such as oculocutaneous albinism (OCA), in autoimmune diseases such as vitiligo, and in melanoma, and may be a modifier locus for primary congenital glaucoma and macular degeneration in X-linked retinoschisis. While tyrosinase activity varies as much as ten-fold in lightly versus darkly pigmented skin, mRNA and protein expression levels are remarkably similar. Instead, post-translational modification of tyrosinase is key for its regulation and activity. Disruption of tyrosinase folding has been implicated in 3 of the 4 major forms of OCA and may contribute to the immune response against melanocytes or melanoma. In Specific Aim 1, we will elucidate the mechanisms underlying post-translational modification of tyrosinase and characterize the roles of the OCA-related proteins as well as protein chaperones in this process. We will also examine the effects of tyrosinase polymorphisms - such as those associated with vitiligo and melanoma risk - on protein folding and enzyme activity. OCA mutations cause accumulation of tyrosinase in the Endoplasmic reticulum (ER), triggering the unfolded protein response (UPR). We have shown that melanocytes adapt to sustained ER stress. In Specific Aim 2, we will continue our investigation of the melanocyte UPR and determine how melanocytes evade apoptosis that is typical of sustained UPR activation. Recent studies suggest that UPR-modulating agents can increase the efficacy of chemotherapeutics. Understanding ER stress and the UPR in melanocytes may thus be critical in the design of adjuvants for melanoma therapies. In Specific Aim 3, we will investigate and assess whether chemical chaperones that promote protein folding improve tyrosinase maturation, particularly in the absence of OCA-related proteins. Such compounds hold promise for the development of therapeutic agents for the OCAs. These studies will greatly advance our understanding of the regulation of skin pigmentation (a major risk factor for skin cancer) and pathogenesis of pigment disorders such as OCA and vitiligo.